\documentclass[letterpaper,10pt]{article}
\usepackage{graphicx}
\begin{document}

\begin{figure}
    \centering
    \includegraphics[scale=1]{cipher.1.mps}
    \caption{cipher.1.mps}
\end{figure}

\begin{figure}
    \centering
    \includegraphics[scale=1]{dif.1.mps}
    \caption{dif.1.mps}
\end{figure}

\begin{figure}
    \centering
    \includegraphics[scale=1]{dif.2.mps}
    \caption{dif.2.mps}
\end{figure}

\begin{figure}
    \centering
    \includegraphics[scale=1]{dif.3.mps}
    \caption{dif.3.mps}
\end{figure}

\begin{figure}
    \centering
    \includegraphics[scale=1]{lin.1.mps}
    \caption{lin.1.mps}
\end{figure}

\begin{figure}
    \centering
    \includegraphics[scale=1]{lin.2.mps}
    \caption{lin.2.mps}
\end{figure}

\end{document}
